Hybrid powertrain and method for controlling the same

Abstract

A method for controlling a hybrid powertrain includes the following steps: (a) receiving, via a control module, a torque request; (b) commanding, via the control module, the first clutch of an automatic transmission to shift to a disengaged position in response to the torque request; (c) commanding, via the control module, an electric motor-generator to transmit torque to an internal combustion engine until a speed of a second clutch is substantially synchronized with a speed of the internal combustion engine; and (d) commanding, via the control module, the second clutch to shift to the engaged position after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. The automatic transmission shifts a transmission speed ratio from an initial speed ratio to a subsequent speed ratio when the second clutch is in the engaged position.

The invention claimed is: 
     
       1. A method of controlling a hybrid powertrain, the hybrid powertrain including an internal combustion engine, an electric motor-generator operatively coupled to the internal combustion engine, an automatic transmission operatively coupled to the internal combustion engine, and the automatic transmission having a first clutch and a second clutch, the method comprising:
 receiving, via a control module, a torque request; 
 commanding, via the control module, the first clutch of the automatic transmission to shift to a disengaged position in response to the torque request; 
 commanding, via the control module, the electric motor-generator to transmit torque to the internal combustion engine until a speed of the second clutch is substantially synchronized with a speed of the internal combustion engine; 
 commanding, via the control module, the second clutch to shift to the engaged position after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine; and 
 wherein the automatic transmission shifts a transmission speed ratio from an initial speed ratio to a subsequent speed ratio when the second clutch is in the engaged position. 
 
     
     
       2. The method of  claim 1 , wherein the hybrid powertrain includes a first and second axle operatively coupled to the internal combustion engine, and the method further comprising determining, via the control module, a current torque in the first and second axles. 
     
     
       3. The method of  claim 2 , wherein the electric motor-generator is a first motor-generator, the hybrid powertrain includes a second electric motor-generator operatively coupled to the second axle, and the method further comprises commanding the second electric motor-generator to increase an output torque thereof while the first clutch is shifting to the disengaged position. 
     
     
       4. The method of  claim 3 , further comprising commanding, via the control module, the second electric motor-generator to decrease the output torque thereof after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       5. The method of  claim 4 , further comprising commanding, via the control module, the first electric motor-generator to decrease an output torque thereof after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       6. The method of  claim 5 , wherein the second electric motor-generator is directly coupled to the second axle, and the method further comprises increasing torque in the second axle when the control module commands the second electric motor-generator to increase the output torque thereof. 
     
     
       7. The method of  claim 6 , wherein the first electric motor-generator is directly coupled to the internal combustion engine, and the method further includes directly transmitting torque from the first electric motor-generator to the internal combustion engine when the control module commands the first electric motor-generator to transmit torque transmit torque to the internal combustion engine until the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       8. The method of  claim 7 , further comprising determining a release rate for the first clutch, wherein the release rate is a rate at which the first clutch moves toward the disengaged position over time. 
     
     
       9. The method of  claim 8 , further comprising determining an apply rate for the second clutch, wherein the apply rate is a rate at which the second clutch moves from the engaged position to the disengaged position over time. 
     
     
       10. The method of  claim 1 , further comprising comparing a shift time with a predetermined time threshold in order to determine if the shift time is less than the predetermined time threshold, wherein the shift time is a time that elapses since the torque request was received by the control module, and the control module commands the first electric motor-generator to transmit torque to the internal combustion engine until the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine only if the shift time is not less than the predetermined time threshold. 
     
     
       11. The method of  claim 10 , wherein the predetermined time threshold is a first predetermined time threshold, and the method further comprises comparing the shift time with a second predetermined time threshold in order to determine if the shift time is less than the second predetermined time threshold, and gradually increasing a torque capacity of the second clutch only if the shift time is less than the second predetermined time threshold. 
     
     
       12. A hybrid powertrain, comprising:
 an internal combustion engine; 
 a first axle operatively coupled to the internal combustion engine; 
 a second axle operatively coupled to the internal combustion engine; 
 a first electric motor-generator operatively coupled to the internal combustion engine; 
 a second electric motor-generator directly coupled to the second axle; 
 an automatic transmission operatively coupled to the internal combustion engine, the automatic transmission including a first clutch and a second clutch; 
 a control module in communication with the internal combustion engine, the first electric motor-generator, the second electric motor-generator, and the automatic transmission, the control module being programmed to:
 receive a torque request; 
 command the first clutch of the automatic transmission to shift to a disengaged position in response to the torque request; 
 command the first electric motor-generator to transmit torque to the internal combustion engine until a speed of the second clutch is substantially synchronized with a speed of the internal combustion engine; 
 command the second clutch to shift to the engaged position after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine; and 
 
 wherein the automatic transmission is configured to shift a transmission speed ratio from an initial speed ratio to a subsequent speed ratio when the second clutch is in the engaged position. 
 
     
     
       13. The hybrid powertrain of  claim 12 , wherein the control module is programmed to determine a current torque in the first and second axles. 
     
     
       14. The hybrid powertrain of  claim 13 , wherein the control module is programmed to command the second electric motor-generator to increase an output torque thereof while the first clutch is shifting to the disengaged position. 
     
     
       15. The hybrid powertrain of  claim 14 , wherein the control module is programmed to command the second electric motor-generator to decrease the output torque thereof after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       16. The hybrid powertrain of  claim 15 , wherein the control module is programmed to command the first electric motor-generator to decrease an output torque thereof after the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       17. The hybrid powertrain of  claim 16 , wherein the second electric motor-generator is configured to increase torque in the second axle when the control module commands the second electric motor-generator to increase the output torque thereof. 
     
     
       18. The hybrid powertrain of  claim 17 , wherein the first electric motor-generator is directly coupled to the internal combustion engine, and the first electric motor-generator is configured to directly transmit torque from the first electric motor-generator to the internal combustion engine when the control module commands the first electric motor-generator to transmit torque to the internal combustion engine until the speed of the second clutch is substantially synchronized with the speed of the internal combustion engine. 
     
     
       19. The hybrid powertrain of  claim 16 , further comprising a torque converter interconnecting the internal combustion engine and the automatic transmission, wherein the first electric motor-generator is continuously coupled to the internal combustion engine.